how to display irrespective length of serial data on Tkinter Window.

This code is to receive serial data and to print on the TKinter window. The received data prints on the window from top to bottom.

My question is @In breif:The font i choose is 37 in my code.with this font size i can print 9 lines on the window. if i receive 1 line of data,this data should print on 5th line, by leaving equal amount of space at top and bottom of the window.Again i may receive 3 line of serial data, this data should print from 4th to 6th line of the window by leaving equal space on top and bottom.Again if i receive 6 lines of serial data, this should print from 2nd line to 7th line on the window. Irrespective of data size, data should print on window,by leaving equal amount of spaces at top and bottom of the window. This display will make a good impression to see on the window. So what i have to do in my code to achieve this kind of display. please help me out. thanks.